I spend most of my free time maintaining both Weather Vane and Audio Switcher, which still run under 10.4 and so can’t make use of any of the new ABI. After looking at a few of the examples of the new stuff on the ‘net, I decided I would try to use them to track multiple NSURLConnections. If you need to create and dispatch multiple, simultaneous NSURLConnections, you’ll find that the  NSURLConnection ABI does not provided a means of distinguishing between the data returned from each connection. One obvious and simple solution to this problem is to subclass NSURLConnection and add some identifying field that distinguishes each connection. I did just this some years back and thought at the time, that it seemed silly to have to do that. So, I thought I’d redo that project specifically using AR’s to track each connection. If you read the docs, you know that you can use AR’s to associate arbitrary data to a given object. When the connection returns data, you inspect the data you associated with it to determine which connection it is and then do whatever you need.

This actually works pretty well, but I wanted to get some opinions from other Cocoa developers about this method of tracking connections. You can read the thread here. Many of the comments were enlightening and gave me a couple more ideas to try. Well, I’ve finally found the time to re-work the project, but this time, instead of trying to shoehorn some ABI into the project, I tried to accomplish this task in a smarter way.

So, this time I decided to wrap an NSURLConnection in an object that acts as the delegate for its connection. This proved to be much cleaner, as now the connection object essentially tracks itself. Of course, this assumes that each connection needs to handle the returned data in the same way. If different connections need to behave differently, you’ll need to try something else. The project creates multiple http request and tracks the time it takes for the headers to come back and then how long it takes for the body of the request to completely load. Not exactly sure if how I time the connections is correct, but it’s neither here nor there for this project. The important part is the connection tracking. Here’s a screen shot:

NSURLConnection timer

Each object is added to an NSArrayController and its fields are mapped to the NSTableView’s columns. Unlike the first project, though, there is no logic in code to determine which connection is which. As the values change in each connection, Cocoa Bindings handles their display, which keeps things nice and clean. You download the project here. There is a file “entries” included with the project. Its just a plist of http urls you can use to populate the table instead of manually typing in urls, if you prefer. I haven’t done a line by line comparison of the two projects, but there is at least 30% reduction in code. I’ve decided not to upload the original project. It  could use a bit of clean up, but if anyone wants to look at it, I’ll go ahead and post it.

As always, if you have ideas or questions, feel free to post.


+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds
invocation:(NSInvocation *)invocation repeats:(BOOL)repeats

+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds
target:(id)target selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)repeats

+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)seconds
target:(id)target selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)repeats

The first two, automatically place the NSTimer in the default runloop, so if you use either of these in this situation, the timer will never fire. Use one of the last two and then you’ll need to manually place the timer in the correct runloop, ala,

[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSModalPanelRunLoopMode];

Of course, when you initialize your timer, you need to give it a method to invoke. Within the body of that method, you can just this send this message to NSApp passing YES as the lone parameter:

- (void)replyToApplicationShouldTerminate:(BOOL)shouldTerminate

I have a sample app here. (The crash issue is now fixed)

One other thing to note is the new “Sudden Termination” feature of Snow Leopard (10.6). To speed up shutdown/restart, the OS will immediately terminate an application if it allows for sudden termination. You can read the documentation here in the:

NSProcessInfo docs.

The upshot of this is that if your app should not abruptly quit (in Snow Leopard), you need to disable sudden termination. You can either do this in code ([[NSProcessInfo processInfo] disableSuddenTermination]) or in the app’s plist (NSSupportsSuddenTermination NO). Whatever route you choose, you can re-enable sudden termination in code via [[NSProcessInfo processInfo] enableSuddenTermination].

That’s it.


NSString *firstCharacterInString = [[self substringToIndex:1] capitalizedString];
NSString *sentenceString = [self stringByReplacingCharactersInRange:NSMakeRange(0,1) withString: firstCharacterInString];



return sentenceString;
}


The only gotcha here, if there is one, is that

(NSString *)stringByReplacingCharactersInRange:(NSRange)range withString:(NSString *)replacement

is Leopard (10.5) and above only, so if you need to support 10.4 (as I do), you need to do something else.

Here’s what I did in Weather Vane:

-(NSString*)stringWithSentenceCapitalization:(NSString*)str
{

return [temp autorelease];
}


As always, if you find a better way, please let me know.

Just a quick post to show how you can get a list of the fonts installed on the iPhone. There are lists available on the internet, but I was bored one day and decided to write an iPhone app that displays them all in a grouped table view subdivided by font family. Its based on some sample code I found here. The only problem with that code is that since it outputs the results to the console, you don’t know how the font actually looks. This little project displays each font string using the font itself. There’s also a simple example of how to create and initialize a table header view from a xib. Here’s the project. Sample output is here:

I hope you find this useful.

Done using iOS 5.1 (should work with older SDK’s and minimum a deployment target of 3.2)

I’m going to assume you can figure out the Cocoa related issues, but the CD issues may not be as straightforward. In particular, when running the second version of the second project, you may get the error: “missing source managed object model”. I only found a couple of references to this error when googling, but because there were so few, and I double and triple checked my code against the book, I assumed the problem must be me. As usual, it was. The simple answer is this: Don’t give your project the exact same name as Zarra does in his book, if you want to also run the projects included in the book’s source code. There is a hash generated when a Core Data project is run and it’s stored in the xml file in the Application Support folder. This hash is used when running a CD project and when migrating a CD data store to a new version. If you run Zarra’s code and the project has the same name, the hash will get changed. If you then attempt the second version of the project with this changed hash, you’ll get the title of this post as an error. If you do get the error, delete the xml file, run the first version of the project and recreate the data. Now you should be able to run the second version of the project and your data will be migrated as expected. I’m sure there are more details that I’m not aware of yet, but this should get you passed this error. I’ll continue to post as I work through the book, so feel free to check in from time to time.

When the initial selection was made in the US table, the notification is sent, the same occurs when a selection is made in the international table. But when the same selection is made again in the US table, the original selection is still valid even though the US table lost focus when the international selection was made, so reselecting it does not trigger an NSTableViewSelectionDidChangeNotification.

When the NSTableViewSelectionDidChangeNotification is sent, an NSTableView delegate method is invoked (if you’ve chosen to be notified of selection changes, or set some class in your project as the NSTableView’s delegate):

- (void)tableViewSelectionDidChange:(NSNotification *)aNotification

My initial attempt to resolve the selection problem tried to handle the problem in this method by deselecting everything in the ‘other’ table (the one losing focus), but what I found is that this led to additional notifications being sent. Every selection triggers a notification AND every deselection triggers a notification as well. One could easily end up with looping notifications this way, which is a problem.

I have a small project which illustrates the problem. You can download it here. (Please note: Although I called the project mutex_tables, one should not confuse this with locks of any sort). The name was determined from the mutually exclusive nature of the tables.

When the tables are initially populated, things look like this:

Once a selection is made, an NSTextField below the tables has its stringValue set (like my location ivar).

After making a selection in the second table, the NSTextField is also updated:

Notice, the selection in the first table, although grayed out since the table has lost focus, is still highlighted.

Now, if we select the same item in the first table, nothing happens. Since technically, there is no change in the selection, the notification is not fired and the text field is not updated.
.

The solution I found is to use another delegate method,

-(BOOL)tableView:(NSTableView*)aTableView shouldSelectRow:(NSInteger)rowIndex

to handle the deselection in the ‘other’ (unfocused) table.

When called, a selection is about to made in one of the tables. What I do then is deselect everything in the ‘other’ table. Now, in tableViewSelectionDidChange, I can just “find” the new selection and update the textfield accordingly. tableViewSelectionDidChange will be called once on the initial selection, and twice thereafter, but never more than twice. Two notifications seem to be unavoidable.

Here’s how things look now after I implemented the new delegate method:

Initial unselected view:

After first selection is made:

After second selection in the other table is made:

But now with our newly implemented delegate method in place, reselecting the original item in the first table, things work properly:

Nothing in the unfocused table is highlighted and as selections are made between the tables, only the current selection in the current table will be highlighted.

Here is my implementation of tableView:shouldSelectRow:

-(BOOL)tableView:(NSTableView*)aTableView shouldSelectRow:(NSInteger)rowIndex{

// Deselecting generates an NSTableViewSelectionDidChangeNotification
// notification.
if (aTableView == self.secondTableView) {
[self.firstTableView deselectAll:self];
}
else {
[self.secondTableView deselectAll:self];
}
return YES;
}

And my tableViewSelectionDidChange
// This will be called once on the initial selection
// twice thereafter.
- (void)tableViewSelectionDidChange:(NSNotification *)aNotification{

NSDictionary * item = nil;
NSUInteger index;

// Make sure we have the right table and ignore no-selection
if([aNotification object] == self.firstTableView && [self.firstController selectionIndex] != NSNotFound){
index = [self.firstController selectionIndex];
item = [self.firstTableArray objectAtIndex:index];
}
else if([aNotification object] == self.secondTableView && [self.secondController selectionIndex] != NSNotFound){
index = [self.secondController selectionIndex];
item = [self.secondTableArray objectAtIndex:index];
}

// When two notifications are sent, item will be nil on first notification
if (item) {
[self.selectionField setStringValue:[item objectForKey:@"test"]];
}
}

You can download the updated project here.

By the way, don’t forget to check the “Avoid Empty Selection” box for the associated NSArrayController.

I hope people find this useful. If someone has a better way, please feel free to comment.